The natural environment, including water and/or soil, may become contaminated with contaminants, illustrative, non-exclusive examples of which include hydrocarbons, organic solvents, pesticides, herbicides, metals, partially halogenated solvents, and partially halogenated organics. These contaminants may be detrimental to a natural ecosystem that may interact with a contaminated region, or contaminated material, and/or may pose health hazards for humans, wildlife, the environment, ecosystems, and/or animals. Microorganisms, such as bacteria and fungi, may consume a portion of these contaminants as part of their natural respiratory processes. This consumption may decompose or degrade the contaminants into less harmful and/or benign respiration products, decreasing contaminant concentration within, or cleaning, the contaminated region, and may take place using aerobic and/or anaerobic reaction pathways. In aerobic respiration, molecular oxygen serves as the ultimate electron acceptor, or oxidant, for the respiratory process, while in anaerobic respiration, another chemical compound serves as the ultimate electron acceptor, or oxidant, for the respiratory process.
Bioremediation is the targeted and deliberate use of these biological, or respiratory, processes to degrade, consume, break down, transform, metabolize, and/or remove contaminants from a treatment zone that is associated with a contaminated region and may be performed both in situ and/or ex situ. In situ bioremediation includes treating the contaminated material without removal from its current, existing, or natural location, while ex situ bioremediation includes removal of the contaminated material from its current, existing, or natural location for treatment on the contaminated site (such as in land farming) or at a different site. Bioremediation processes that include the introduction of reactants for the respiration process, such as oxidants and/or nutrients, into the treatment zone to enhance, assist, augment, stimulate, and/or promote the growth of native microorganisms that are already present within the contaminated region are termed bio-stimulation processes, while bioremediation processes that include the introduction of non-native microorganisms into the treatment zone, with or without the introduction of oxidants and/or nutrients, are termed bio-augmentation processes.
For bioremediation to occur, a contaminated region must include a microbial population that is adapted to metabolize a contaminant, as well as an energy source, a carbon source, an electron acceptor (or oxidant), nutrients, and suitable environmental conditions. The microbial population may include native microbes and/or may include specialized microbes that may be added to the treatment zone during a bio-augmentation process. The contaminant is typically utilized by the microbial population as both the energy source and the carbon source, providing the mechanism by which the bioremediation processes may decrease a contaminant concentration within the treatment zone.
Once a suitable microbial population is present within the treatment zone, bio-stimulation processes may be utilized to increase a rate of contaminant consumption by the microbial population, such as by providing a source of oxidants and/or nutrients and/or by providing an environment that is more suitable for microbial growth. Illustrative, non-exclusive examples of environmental conditions that may impact microbial growth may include the temperature, pH, salinity, pressure, contaminant concentration, and/or an inhibitor concentration within the treatment zone.